Method of manufacturing a sintered metal tube



1964- M EUDIER 3, 5 8

METHOD OF MANUFACTURING A SINTERED METAL TUBE Filed Feb. 24, 1961 IN VEN TOE MICHEL E 1/0/52 A TTOENEYS United States Patent 3,159,482 METHODOF MANUFACTURING A SHQTERED METAL TUBE Michel Earlier, 3 Rue Andrieux,Paris, France Filed Feb. 24, 1961, Ser. No. 91,348 Claims priority,application France Mar. 11, 1960 Claims. (Cl. 75-200) The presentinvention concerns the manufacture of porous or non-porous tubes, havinga density equal to or less than the density of the metal used, bysintering metallic powders.

The manufacture of tubes from sintered metal presents several difficultproblems, particularly with regard to preserving the shape of the tubewhile applying heat during the sintering process.

On the other hand, sintering devices should be designed in such a waythat the tubes, while still unsintered, do not break.

According to the method of the present invention, the tube is firstformed by the agglomeration of a metallic powder with a binder, and isthen placed in aninclined position, rotated substantiallyabout its axisand heated starting from the lower part of the tube.

The invention also includes an apparatus for manufacturing tubes fromsintered metal, which comprises an inclined refractory tube forcontaining a tube formed of a mixture of a metal powder and a bindingagent, the inner diameter of the refractory tube being at least 0.5 mm.greater than the outer diameter of the metal powder tube, a motor forrotating the refractory tube about its axis and an annular furnacesurrounding the refractory tube and arranged to undergo displacementupwardly along the refractory tube during the sintering process.

The inclination of the outer tube is preferably such that the angleformed by it with the horizontal plane is between 5 and 30; in this way,the sinter tube is prevented from sliding relative to the outer tube.Moreover, since there is a clearance between the sinter tube and theouter tube and the former rests on the latter substantially along one ofits generatrices, the frictional forces between the two tubes aredecreased because of the inclination, although for inclinations lessthan 5 these frictional forces could be sufiicient to produce fractureof the tube into several pieces when the inner sinter tube shrinks. Themaximum angle of inclination depends principally on the nature of thesurfaces in contact (the sinter tube and the outer tube). If the outertube is ridged, for example, this maximum'angle of inclination can beincreased, since there is less tendency for sliding of the sinter tuberelative to the outer tube.

The outer diameter of the sinter tube is less than the inner diameter ofthe outer tube by an amount sufiicient to prevent their coincidenceduring sintering, and to en able the sinter tube to roll inside theouter tube during the rotation of the latter. The clearance between thetwo positioned tubes, namely the difference between the two diametersmentioned, should be at least 0.5 mm.

The inner tube undergoes shrinkage during sintering and becomes ovalshaped if it does not rotate, that is to say, if the outer tube does nottransmit its own rotary movement thereto. Because of this rotation, theformation of an oval shape is completely prevented. The speed vofrotation v of the outer tube should be a minimum of the order of lrevolution during the period of sintering; since the speed can varybetween 10 minutes and one hour, particularly according to the natureof'the sintering powder and temperature chosen, it can be seen that theminimum speed of rotation is of the order of l to 6 revolutions perhour; the maximum value of the speed of rotation is limited only by theresistance to vibration of the sinter tube, but there is no purpose intrying to should be a fraction (not more than half) of the length of theouter tube. According to the importance of the length of this zone, itsspeed of displacement v will conform more or less to the formula v=L/ t,where t is the duration of sintering (between 10 minutes and an hour).As the length of this zone is dependent upon the means being used toproduce it and consequently has a minimum value (5 cm. in the case of amovable electric resistance furnace), there are minimum and maximumvalues for the speed v; the minimum value will be equal to 5 cm. perhour in the case where the furnace is 5 cm. in length; in the same caseand with an outer tube of 110 cm. in length, the heating zone may have amaximum length of about 55 cms. and the value of v will be in the regionof 330 cur/hour.

The reason for producing progressive displacement of the heating zone isthat the zone in which the binding material iseliminated (in the partbelow the sinter zone) is of small dimensions and moves progressively insuch a way that, in contrast to methods in which the binding material iseliminated simultaneously over an extended zone in the inner tube, itcannot produce fractures of the tube during sintering. Furthermore, asthe zone in which a longitudinal shrinkage of the sinter tube isproduced at a given moment corresponds to the sinter zone and does notcover the entire length of the inner tube, fractures are prevented whichresult when the shrinkage occurs at the same moment on all parts of thetube. I In order that the invention may be more readily understood, thepreferred embodiment thereof is described 7 below in conjunction withthe accompanying drawing,

which shows an elevational view, partly in section of one form ofapparatus for manufacturing tubes.

The apparatus comprises a tube 1 of stainless or re-' 1 in mesh with apinion 5 driven by a reduction motor.

The speed of rotation of the tube 1 about its axis is in the region ofone revolution per minute. A tube 6 which is cm. long is mounted insidethe tube 1, which has a length of cm., and the tube 6 is formed by metalpowder agglomerated by a binder, for example collodion.

This tube may be formed by many different methods, for

example by centrifugal action and drying or by extruson.

A clearance of 1 mm. is left between the adjacent walls of tubes 1 and 6to accommodate the tube 6, which has an outer diameter for examplebetween 5 and 25 mm.

When the tube 6 is located inside the tube 1, a conduit 7 is introducedinto the upper end of the tube 1 for supplying a stream ofhydrogen intothe latter or, in general, any reducing gas (or a vacuum may be providedin tube 1); the gas is burnt at the lower end of the tube 1.

The sintering heating is effected by a furnace 8 initially disposed atthe lower end of the tube 1 and provided with driving means of a knowntype (endless screw for ex to the rotation (the speed of rotation v '=60revs/hour),

formation-oftheoval shape is completely avoided. Moreover, the sinteredtube is fully protected during the sintering operation (in particularmechanical protection is providedbythe outer'tube 1) thatis to'say,during'the time at which the tube is the most fragile.

The speed of displacement'v of the furnaces (length L ofthe furnace=20cms) "is of the order of 1 metre an hour which corresponds to a durationof sintering of 12 minutes '(the fpitch of the helix described by apoint on the region of the sintered'tube situated at the intersection ofonegeneratrix of this tube and of the zone of sintering is'thus equal to1.65 cm.).

During the sintering, the collodion or other binding agent is destroyedby'the heating and the metallic powder forming the tubeGbecomessintered. The gases formed by destruction of'the'binding agent areevacuated at the same time as'theexcess hydrogen.

'Of course, the invention is not limited by the details of the methoddescribed, the expert being able to modify these methods, withinthescope of the invention. The nature of the metal comprising the sinterpowder and the 'nature of the binding agent may be varied. Such metalsare, for example, iron, bronze and'nickel, and the binding agent may becollodion, polyvinyl alcohol in water orgum tragacanth in water.

What'I claim is:

1. A method of manufacturing a sintered metal tube, which comprisesforming a mixture of powdered metal and a binding agent into a tubularshape, locating the thus-formedmetal powder tube with a clearance in anouter tube of refractory material disposed at an angle to thehorizontal, the clearance between the metal powder tube and the outertube being sufiicient to prevent their coincidence during sintering,rotating the outer tube about its'l'ongitudinal axis at a speed ofrotation corresponding'to 'at'least 'one'revolution during the period ofthe sintering thereby rolling the powder metal tube inside the outertube during rotation of the latter tube, and.

supplying'heat to sinter the metal powder tube.

2. A method as claimed in claim 1, in which the heating step is*elfected by a heat source which is moved longitudinally along saidrefractory tube'fromthe lower portion thereof to the upper portionthereof during the period of sintering.

3. A method as claimed in claim 2, in which said heat source is moved soas to provide an overall sintering time of 10 to minutes.

4. A method as claimed in claim 1, in which the refractory tube isdisposed at an inclination of 5 to 30 to the horizontal.

5. A method as claimed in claim 1, in which the sintering temperature is600 to 1200 C.

6. A method as claimed in claim 1, in which the clearance between themetal powder tube andthe refractory tube is at least 0.5mm.

7. A method as claimed in claim 1, in which the speed of rotation of therefractory tube is up to 5 revolutions per hour.

8. A method as claimed in claim 1, in which a stream of hydrogen orother.reducing'gasis'passed through'the refractory tube duringsintering.

9Q A metho'd as claimed in claim 1, in which the binding agent isselected from the group consistingof collodion, polyvinyl alcohol andgum tragacanth.

10. A method as claimed in claim 1, in which the'metal powder isselected from the group consisting of iron,

bronze and nickel.

References Cited in the file of this patent UNITED STATESPATENTS1,226,470 Coolidge May 15,1917 1,531,666 Laise Mar. 31, 1925 2,372,203Hensel et al Mar. 27, 1945 2,431,690 Hall et al. Dec. 2, 1947 2,930,098Emeis Mar. 29, 1960 2,936,505 \Vitucki et a1 May 17, 1960 FOREIGNPATENTS 1,077,511 Germany "Mar..10, 1960 1,237,168 France June 20, 1960OTHER REFERENCES AEC Document TID 7546, Book 2, November 1957, pp. 532and 533.

1. A METHOD OF MANUFACTURING A SINTERED METAL TUBE, WHICH COMPRISESFORMING A MIXTURE OF POWDERED METAL AND A BINDER AGENT INTO A TUBULARSHAPE, LOCATING THE THUS-FORMED METAL POWDER TUBE WITH A CLEARANCE IN ANOUTER TUBE OF REFRACTORY MATERIAL DISPOSED AT AN ANGLE TO THEHORIZONTAL, THE CLEARANCE BETWEEN THE METAL POWDER TUBE AND THE OUTERTUBE BEING SUFFICIENT TO PREVENT THEIR COINCIDENCE DURING SINTERING,ROTATING THE OUTER TUBE ABOUT ITS LONGITUDINAL AXIS AT A SPEED OFROTATION CORRESPONDING TO AT LEAST ONE REVOLUTION DURING THE PERIOD OFTHE SINTERING THEREBY ROLLING THE POWDER METAL TUBE INSIDE THE OUTERTUBE DURING ROTATION OF THE LATTER TUBE, AND SUPPLYING HEAT TO SINTERTHE METAL POWDER TUBE.